/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.fn.harness.state;



import com.bff.gaia.unified.vendor.guava.com.google.common.collect.Iterables;



import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import java.util.NoSuchElementException;



/**

 * Converts an iterator to an iterable lazily loading values from the underlying iterator and

 * caching them to support reiteration.

 */

class LazyCachingIteratorToIterable<T> implements Iterable<T> {

  private final List<T> cachedElements;

  private final Iterator<T> iterator;



  public LazyCachingIteratorToIterable(Iterator<T> iterator) {

    this.cachedElements = new ArrayList<>();

    this.iterator = iterator;

  }



  @Override

  public Iterator<T> iterator() {

    return new CachingIterator();

  }



  /** An {@link Iterator} which adds and fetched values into the cached elements list. */

  private class CachingIterator implements Iterator<T> {

    private int position = 0;



    private CachingIterator() {}



    @Override

    public boolean hasNext() {

      // The order of the short circuit is important below.

      return position < cachedElements.size() || iterator.hasNext();

    }



    @Override

    public T next() {

      if (position < cachedElements.size()) {

        return cachedElements.get(position++);

      }



      if (!iterator.hasNext()) {

        throw new NoSuchElementException();

      }



      T rval = iterator.next();

      cachedElements.add(rval);

      position += 1;

      return rval;

    }

  }



  @Override

  public int hashCode() {

    return iterator.hasNext() ? iterator.next().hashCode() : -1789023489;

  }



  @Override

  public boolean equals(Object obj) {

    return obj instanceof Iterable && Iterables.elementsEqual(this, (Iterable) obj);

  }



  @Override

  public String toString() {

    return Iterables.toString(this);

  }

}